I. Field of the Invention.
This invention relates generally to an electrosurgical generator having characteristics which enhance electrosurgical procedures.
II. Discussion of the Prior Art.
By now, electrosurgical procedures have become quite common and various systems are presently on the market for allowing radio frequency power to be delivered to a cutting blade, or a forceps or other implement whereby cutting of tissue or coagulation of blood can be selectively accomplished by the mere depression of appropriate control switches by the surgeon. A concise discussion of the underlying principles relating to electrosurgery is set out in the introductory portion of the Bowers U.S. Pat. No. 4,559,943, which is hereby incorporated by reference.
In the Stasz U.S. Pat. No. 4,674,498, which is assigned to applicants, assignee, there is described an electrosurgical system in which the electrosurgical blade is made to vibrate at a frequency sufficient to cause cavitation to take place as rf energy is simultaneously applied to electrodes on the blade for effecting cutting and coagulation. The high frequency vibrations of the blade have been found to markedly reduce the buildup of charred blood and tissue on the electrosurgical blade which obviates the need for frequent cleaning and/or blade replacement. The present invention is directed to an electrosurgical generator which has been specially designed to power the electrodes on electrosurgical implements while at the same time powering the transducer used to impart vibratory motion to the implement.
The electrosurgical generator of the present invention includes at least two channels, whereby more than one electrosurgical implement can be operated by a surgeon or by a surgeon and an assistant. For example, an electrosurgical scalpel of the type including a blade supported in a handle may be connected by a cable to a first channel of the generator and, by manipulating finger switches on the handle, appropriate rf energy for either cutting or coagulating may be delivered to the appropriate electrodes disposed on the scalpel blade while the blade is simultaneously vibrated. The other channel may be used in a typical situation to deliver rf energy to a bipolar forceps upon the actuation of a foot switch, also coupled to the electrosurgical generator. One or both of the implements may be simultaneously powered.
When using an electrosurgical scalpel, the impedance presented to the electrodes is found to vary depending upon the body fluids and tissue types encountered. For example, as the blade is made to pass through blood, the impedance between the blade's electrodes would be relatively low as compared to when skin and muscle tissue is encountered. Likewise, fat tissue is found to present a higher impedance than skin and muscle tissue. To avoid the necessity of frequently adjusting manual controls on the electrosurgical generator to vary the power output in accordance with the tissue being encountered, the electrosurgical generator of the present invention includes a novel feedback control network for maintaining the power output relatively flat over a wide load impedance range.
It has also been found that cleaning is enhanced where the energy used to drive the ultrasonic transducer is effectively synchronized with the rf power being delivered to the electrosurgical electrodes. Moreover, by keying the signal delivered to the ultrasonic transducer on and off at a rate which is related to the natural resonant frequency of the blade and handle combination, enhanced cleaning takes place, presumably due to an increase in the amplitude of the displacement of the vibrating blade.
The repeated switching on and off of the power being delivered to the blade in prior art electrosurgical generators has also been a rich source of electromagnet interference (EMI) which could adversely affect other electronic instrumentation found in an operating room setting. To reduce EMI, in accordance with the present invention, the turning on and off of the rf power is synchronized with the zero crossing of the rf waveform such that switching occurs when the instantaneous AC power is zero.